Various types of analytical tests related to patient diagnosis and therapy can be performed by analysis of a liquid sample taken from a patient's bodily fluids, or abscesses. These assays are typically conducted with automated clinical analyzers onto which tubes or vials containing patient samples have been loaded. The analyzer extracts a liquid sample from the vial and combines the sample with various reagents in special reaction cuvettes or tubes (referred to generally as reaction vessels). Usually the sample-reagent solution is incubated or otherwise processed before being analyzed. Analytical measurements are often performed using a beam of interrogating radiation interacting with the sample-reagent combination, for example, turbidimetric, fluorometric, absorption readings, or the like. The measurements allow determination of end-point or rate values from which an amount of analyte related to the health of the patient may be determined using well-known calibration techniques.
Clinical chemistry analyzers employ many different processes to identify analytes and, throughout these processes, patient liquid samples and samples in combination with various other liquids (such as reagents, diluents, or re-hydrated compositions) are frequently required to be mixed to a high degree of uniformity. Due to increasing pressures on clinical laboratories to increase analytical sensitivity, there continues to be a need for improvements in the overall processing efficiency of clinical analyzers. In particular, sample analysis continuously needs to be more effective in terms of increasing assay throughput. There remains a need for sample-reagent mixers that mix a liquid solution to a high degree of uniformity at very high speed without unduly increasing analyzer cost or requiring a disproportional amount of time or space.
Various methods have historically been implemented to provide a uniform sample solution mixture including agitation, stirring/mixing, ball milling, etc. One popular approach involves using a pipette to alternately aspirate and release a portion of liquid solution within a liquid container. Magnetic mixing, in which a vortex mixing action is introduced into a solution of liquid sample and liquid or non-dissolving reagents, has also been particularly useful in clinical and laboratory devices.
U.S. Pat. No. 6,382,827 discloses a method for mixing a liquid solution contained in a liquid container by causing a freely disposed, spherical mixing member to rapidly oscillate within the solution in a generally circular pattern within the container. The spherical mixing member is caused to rapidly move within the solution by revolving a magnetic field at high speed in a generally circular pattern in proximity to the liquid container. Magnetic forces acting upon the magnetic mixing member cause it to generate a mixing motion within the liquid solution.
U.S. Pat. No. 7,258,480, assigned to the assignee of the present application and incorporated herein by reference, discloses a mixing device for mixing solutions within a biochemical analyzer by moving a sampling probe needle in a two-dimensional, generally parabolic or generally “boomerang-shaped” mixing pattern of the probe needle.
Methods that rely on a mechanical stirring motion, such as that disclosed in U.S. Pat. No. 7,258,480, can be sensitive to the vertical location of the stirring element. For example, when placed too high relative to the bottom of the cuvette (or other reaction vessel), the stirring element will not stir the solution efficiently, requiring more time and motion or causing an incomplete mixture. Likewise, when placed too low relative to the bottom of the cuvette, the stirring element can impact the bottom or any sloped sides of the cuvette or otherwise become stuck or damped, and provide an ineffective or failed mix. However, many apparatus that use mechanical stirring to mix a solution rely on either a fixed height for a stirring element, which may be changed when a mixing element (e.g., a probe needle) is installed, or they require a manual estimation of the height of the tip of the stirring element. Such approaches may be prone to mechanical failure or operator error.
Thus, there continues to be a need for an improved approach to the design of a simplified, space-efficient, liquid sample and/or sample-reagent mixer. In particular, there is a continuing need for an improved sample-reagent solution mixer with a reliable means for adjusting the height of the mixing element, such that the mixer provides high speed and mixing of solutions contained in reaction vessels with a very high degree of uniformity in a desirably small amount of time and space.